1. Field of the Invention
The invention relates to a steering control system.
2. Description of the Related Art
There are known electric power steering systems (EPS) that assist a driver's steering operation by applying motive power generated by a motor to a steering mechanism of a vehicle. An electric power steering system (EPS) described in, for example, Japanese Patent Application Publication No. 2014-40178 (JP 2014-40178 A) calculates a controlled variable associated with driver's steering, based on a steering torque generated through the driver's steering.
Recent vehicles are equipped with systems for assisting a driver's operation, such as advanced driver assistance systems (ADAS). Some electric power steering systems (EPS) mounted in such vehicles control a motor based on a controlled variable associated with driver's steering and a controlled variable calculated based on an environment surrounding a host vehicle, which is measured by a measuring apparatus, such as a camera or a radar, in order to improve a driver's steering feel and to provide advanced driver assistance.
When the steering angle of a steering mechanism is varied through driver assistance, a torsion bar is twisted due to viscosity and inertia of a steering wheel. Consequently, a steering torque unassociated with the driver's steering is detected. Therefore, when the EPS calculates a controlled variable associated with the driver's steering, the EPS takes into account a steering torque generated through the driver assistance in addition to a steering torque generated through the driver's steering. The controlled variable associated with the driver's steering and the controlled variable associated with the driver assistance interfere with each other, and the follow-up accuracy with which the steering angle follows a steering angle command value may be reduced accordingly.